The present invention relates to a wax-pellet termostat for automotive engines.
The conventional wax-pellet thermostat comprises a thermo-sensitive device and a valve device. The thermo-sensitive device includes a steel piston, a guide member slidably engaged with the piston, a rubber diaphragm around the piston, and a wax. The piston is sealed by a sealing device provided in the guide member. However, if the sealing device deteriorates, a space in the diaphragm is communicated with a coolant passage. Under such a condition, when the temperature of coolant rapidly decreases from high temperature (about 100.degree. C.) to low temperature(below 40.degree. C.), the space in the diaphragm becomes a vacuum. Accordingly, the coolant is inducted into the space. Since the diaphragm tightly grips the piston, the coolant in the space cannot be discharged. As described hereinafter, the valve is slightly raised by the coolant in the space, which causes the opening temperature of the valve to decrease. As a result, the engine is overcooled, thereby reducing the thermal efficiency of the engine and increasing the amount of emissions. The amount of the coolant in the space increases with time, so that the valve lift increases, which causes engine trouble.